The insurgents attacked the group in Zabul province, The New York Times reported, quoting Afghan officials. Another seven guards were injured in the Tuesday attack, one of the worst in recent months, the report said.

The workers were ambushed as they were surveying a new road leading to the hilly regions used as a haven by the insurgents from Pakistan.

The Times report said the crew and their guards were moving in a convoy through a valley when the militants opened fire on them.

Muhammad Younus, project manager for the Fazlullah Construction Engineering Co., said none of the construction crew was hurt because of the protection provided by the guards, who fought the militants until a unit of the Afghan Army arrived.

Deputy Gov. Gulab Shah Ali Kheil said the army unit killed and wounded several of the militants in the ensuing battle.

There is growing concern there may be more such attacks with the start of the warmer weather, the report said.